1. Field
The example embodiments relate to a technique that may measure a location of a moving object by using ultrasound.
2. Description of the Related Art
Recently, there has been increased attention to a technique of measuring a three-dimensional (3D) location of a moving substance or a moving object, as a motion sensing scheme is utilized for a movie, game, and the like.
Examples of a method of estimating or measuring the 3D location of the moving substance or the moving object may include a method using ultrasound.
Ultrasound travels through the air at about 340 m/s. Accordingly, when a time of flight (TOF) of the ultrasound from an ultrasound transmitting unit to the moving object is measured by using a characteristic of the ultrasound, a distance between the ultrasound transmitting unit and the moving object may be calculated.
When distance information of distances between at least three ultrasound transmitting units and the moving object is obtained by using the at least three ultrasound transmitting units, the 3D location of the moving object may be measured by using triangulation based on the distance information.
A speed of the ultrasound is relatively slow. Therefore, when the location of the moving object is measured by a plurality of ultrasound transmitting units, the plurality of ultrasound transmitting units may need to sequentially transmit the ultrasound in consideration of the speed of the ultrasound.
When the plurality of ultrasound transmitting units simultaneously transmit the ultrasound, interference may occur between the transmitted ultrasound signals.
In general, although the plurality of ultrasound transmitting units sequentially transmit ultrasound, the 3D location of the moving object may be relatively accurately measured when the moving object is fixed in a predetermined location. However, when the moving object moves quickly, there may be an error in measuring of the 3D location of the moving object since obtained distance information of distances between the plurality of ultrasound transmitting units and the moving object is not measured at a same point in time.
In general, examples of a method of measuring a location of a moving object by using an ultrasound may include a method using a triangulation through at least three ultrasound transmitting units.
The location measuring method may transmit the ultrasound to the moving object by using at least three ultrasound transmitting units, may obtain distance information of distances between the moving object and the at least three ultrasound transmitting units based on a time in which the moving object receives the ultrasound, and may perform triangulation based on the distance information, thereby calculating a three-dimensional (3D) location of the moving object.
The location measuring method may relatively accurately measure the location, when the moving object is fixed in a predetermined location, whereas the location measuring method may not accurately measure the location when the moving object moves quickly.
When the moving object moves, the distance information of distances between the moving object and the at least three ultrasound transmitting units may not be measured at a same point in time, since the ultrasound is sequentially transmitted from the at least three ultrasound transmitting units.
As an example, the ultrasound in a related art is sequentially transmitted from the at least three ultrasound transmitting units, in an order of an ultrasound transmitting unit 1, an ultrasound transmitting unit 2, and an ultrasound transmitting unit 3.
The assumption is for convenience of description, and the ultrasound may not be necessarily transmitted in the order of the ultrasound transmitting unit 1, the ultrasound transmitting unit 2, and the ultrasound transmitting unit 3. That is, the ultrasound is sequentially transmitted from a plurality of ultrasound transmitting units, and a transmission sequence may be different depending on the circumstances.
Here, it is assumed that the ultrasound transmitting unit 1 transmits the ultrasound to the moving object at a point in time t-2, the ultrasound transmitting unit 2 transmits the ultrasound to the moving object at a point in time t-1, and the ultrasound transmitting unit 3 transmits the ultrasound to the moving object at a point in time t.
To measure a location of the moving object at the point in time t, distance information of a distance between the moving object and the ultrasound transmitting unit 1 of the point in time t, distance information of a distance between the moving object and the ultrasound transmitting unit 2 of the point in time t, and distance information of a distance between the moving object and the ultrasound transmitting unit 3 of the point in time t may be used.
However, the distance information of the distance between the ultrasound transmitting unit 1 and the moving object is distance information of the point in time t-2, the distance information of the distance between the ultrasound transmitting unit 2 and the moving object is distance information of the point in time t-1, and the distance information of the distance between the ultrasound transmitting unit 3 and the moving object is distance information of the point in time t. Accordingly, when the location of the moving object is calculated based on the distance information of the distances, an error may occur.
A method of simultaneously transmitting the ultrasound from the plurality of ultrasound transmitting units may be used to prevent the error. However, interference may occur between the simultaneously transmitted ultrasound signals, and thus, the method is practically unavailable.
Accordingly, there is a need for a method for minimizing the error, when the location of the moving object is measured by the plurality of ultrasound transmitting units.
Accordingly, example embodiments perform, based on an inertial navigation, a time synchronization that converts distance information of distances between the moving object and the ultrasound transmitting units at a point prior to a current point in time into distance information at the current point in time, thereby accurately measuring the location of the moving object at the current point in time.